Identifying the sex of your Goldfish can be slightly tricky, especially when they’re young. As they mature, males typically develop tiny, white tubercles on their gills or pectoral fins during breeding, while females grow slightly plumper.
Also, a male Goldfish’s rear side, where the abdomen meets the tail of the fish, is usually more streamlined compared to the female’s more rounded one. Determining the sex accurately may require a bit of experience and closer observation, as these differences are quite subtle.